Chemistry Unit 2: Energy

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Enthalpy
Enthalpy is the heat content that is stored in a chemical system.
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Exothermic
Exothermic refers to a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings.
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Endothermic
Endothermic refers to a reaction in which the enthalpy of the reactants, resulting in heat being taken in from the surroundings.
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Enthalpy Profile Diagram
An enthalpy profile diagram is a diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products.
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Activation Energy
Activation energy is the minimum energy required to start a reaction by the breaking of bonds.
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Standard Conditions
Standard conditions are a pressure of 100kPa (1 atmosphere), a temperature of 298K (25°C) and a concentration of 1.0 mol dm-3.
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Standard State
Standard state is the physical state of a substance under the standard conditions of 100 kPa (1 atmosphere) and 298K (25°C).
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Standard Enthalpy Change of Reaction
The standard enthalpy change of reaction is the enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.
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Standard Enthalpy Change of Combustion
The standard enthalpy change of combustion is the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states.
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Standard Enthalpy Change of Formation
The standard enthalpy change of formation of a compound is the enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.
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Specific Heat Capicity
Specific heat capacity is the energy required to raise the temperature of 1 g of a substance by 1°C.
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Bond Enthalpy
Bond enthalpy is the enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecules of a gaseous species.
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Average Bond Enthalpy
Average bond enthalpy is the average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species.
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Hess' Law
Hess' law states that, if a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.
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Enthalpy Cycle
An enthalpy cycle is a diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess' law.
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Rate of Reaction
The rate of reaction is the change in concentration of a reactant or a product in a given time.
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Heterogeneous Catalysis
Heterogeneous catalysis is catalysis of a reaction in which the catalyst has a different physical state from the reactants; frequently, reactants are gases whilst the catalyst is a solid.
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Homogeneous Catalysis
Homogeneous catalysis is catalysis of a reaction in which the catalyst and reactants are in the same physical state, which is most frequently aqueous or gaseous state.
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Dynamic Equilibrium
Dynamic equilibrium is the equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction.
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le Chatelier's Principle
le Chatelier's principle states that when a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change.
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Card 2

Front

Exothermic refers to a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings.

Back

Exothermic

Card 3

Front

Endothermic refers to a reaction in which the enthalpy of the reactants, resulting in heat being taken in from the surroundings.

Back

Preview of the back of card 3

Card 4

Front

An enthalpy profile diagram is a diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products.

Back

Preview of the back of card 4

Card 5

Front

Activation energy is the minimum energy required to start a reaction by the breaking of bonds.

Back

Preview of the back of card 5
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